mirror of https://github.com/Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
635 lines
17 KiB
635 lines
17 KiB
/* |
|
* trace_hwlatdetect.c - A simple Hardware Latency detector. |
|
* |
|
* Use this tracer to detect large system latencies induced by the behavior of |
|
* certain underlying system hardware or firmware, independent of Linux itself. |
|
* The code was developed originally to detect the presence of SMIs on Intel |
|
* and AMD systems, although there is no dependency upon x86 herein. |
|
* |
|
* The classical example usage of this tracer is in detecting the presence of |
|
* SMIs or System Management Interrupts on Intel and AMD systems. An SMI is a |
|
* somewhat special form of hardware interrupt spawned from earlier CPU debug |
|
* modes in which the (BIOS/EFI/etc.) firmware arranges for the South Bridge |
|
* LPC (or other device) to generate a special interrupt under certain |
|
* circumstances, for example, upon expiration of a special SMI timer device, |
|
* due to certain external thermal readings, on certain I/O address accesses, |
|
* and other situations. An SMI hits a special CPU pin, triggers a special |
|
* SMI mode (complete with special memory map), and the OS is unaware. |
|
* |
|
* Although certain hardware-inducing latencies are necessary (for example, |
|
* a modern system often requires an SMI handler for correct thermal control |
|
* and remote management) they can wreak havoc upon any OS-level performance |
|
* guarantees toward low-latency, especially when the OS is not even made |
|
* aware of the presence of these interrupts. For this reason, we need a |
|
* somewhat brute force mechanism to detect these interrupts. In this case, |
|
* we do it by hogging all of the CPU(s) for configurable timer intervals, |
|
* sampling the built-in CPU timer, looking for discontiguous readings. |
|
* |
|
* WARNING: This implementation necessarily introduces latencies. Therefore, |
|
* you should NEVER use this tracer while running in a production |
|
* environment requiring any kind of low-latency performance |
|
* guarantee(s). |
|
* |
|
* Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <[email protected]> |
|
* Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <[email protected]> |
|
* |
|
* Includes useful feedback from Clark Williams <[email protected]> |
|
* |
|
* This file is licensed under the terms of the GNU General Public |
|
* License version 2. This program is licensed "as is" without any |
|
* warranty of any kind, whether express or implied. |
|
*/ |
|
#include <linux/kthread.h> |
|
#include <linux/tracefs.h> |
|
#include <linux/uaccess.h> |
|
#include <linux/cpumask.h> |
|
#include <linux/delay.h> |
|
#include "trace.h" |
|
|
|
static struct trace_array *hwlat_trace; |
|
|
|
#define U64STR_SIZE 22 /* 20 digits max */ |
|
|
|
#define BANNER "hwlat_detector: " |
|
#define DEFAULT_SAMPLE_WINDOW 1000000 /* 1s */ |
|
#define DEFAULT_SAMPLE_WIDTH 500000 /* 0.5s */ |
|
#define DEFAULT_LAT_THRESHOLD 10 /* 10us */ |
|
|
|
/* sampling thread*/ |
|
static struct task_struct *hwlat_kthread; |
|
|
|
static struct dentry *hwlat_sample_width; /* sample width us */ |
|
static struct dentry *hwlat_sample_window; /* sample window us */ |
|
|
|
/* Save the previous tracing_thresh value */ |
|
static unsigned long save_tracing_thresh; |
|
|
|
/* NMI timestamp counters */ |
|
static u64 nmi_ts_start; |
|
static u64 nmi_total_ts; |
|
static int nmi_count; |
|
static int nmi_cpu; |
|
|
|
/* Tells NMIs to call back to the hwlat tracer to record timestamps */ |
|
bool trace_hwlat_callback_enabled; |
|
|
|
/* If the user changed threshold, remember it */ |
|
static u64 last_tracing_thresh = DEFAULT_LAT_THRESHOLD * NSEC_PER_USEC; |
|
|
|
/* Individual latency samples are stored here when detected. */ |
|
struct hwlat_sample { |
|
u64 seqnum; /* unique sequence */ |
|
u64 duration; /* delta */ |
|
u64 outer_duration; /* delta (outer loop) */ |
|
u64 nmi_total_ts; /* Total time spent in NMIs */ |
|
struct timespec timestamp; /* wall time */ |
|
int nmi_count; /* # NMIs during this sample */ |
|
}; |
|
|
|
/* keep the global state somewhere. */ |
|
static struct hwlat_data { |
|
|
|
struct mutex lock; /* protect changes */ |
|
|
|
u64 count; /* total since reset */ |
|
|
|
u64 sample_window; /* total sampling window (on+off) */ |
|
u64 sample_width; /* active sampling portion of window */ |
|
|
|
} hwlat_data = { |
|
.sample_window = DEFAULT_SAMPLE_WINDOW, |
|
.sample_width = DEFAULT_SAMPLE_WIDTH, |
|
}; |
|
|
|
static void trace_hwlat_sample(struct hwlat_sample *sample) |
|
{ |
|
struct trace_array *tr = hwlat_trace; |
|
struct trace_event_call *call = &event_hwlat; |
|
struct ring_buffer *buffer = tr->trace_buffer.buffer; |
|
struct ring_buffer_event *event; |
|
struct hwlat_entry *entry; |
|
unsigned long flags; |
|
int pc; |
|
|
|
pc = preempt_count(); |
|
local_save_flags(flags); |
|
|
|
event = trace_buffer_lock_reserve(buffer, TRACE_HWLAT, sizeof(*entry), |
|
flags, pc); |
|
if (!event) |
|
return; |
|
entry = ring_buffer_event_data(event); |
|
entry->seqnum = sample->seqnum; |
|
entry->duration = sample->duration; |
|
entry->outer_duration = sample->outer_duration; |
|
entry->timestamp = sample->timestamp; |
|
entry->nmi_total_ts = sample->nmi_total_ts; |
|
entry->nmi_count = sample->nmi_count; |
|
|
|
if (!call_filter_check_discard(call, entry, buffer, event)) |
|
__buffer_unlock_commit(buffer, event); |
|
} |
|
|
|
/* Macros to encapsulate the time capturing infrastructure */ |
|
#define time_type u64 |
|
#define time_get() trace_clock_local() |
|
#define time_to_us(x) div_u64(x, 1000) |
|
#define time_sub(a, b) ((a) - (b)) |
|
#define init_time(a, b) (a = b) |
|
#define time_u64(a) a |
|
|
|
void trace_hwlat_callback(bool enter) |
|
{ |
|
if (smp_processor_id() != nmi_cpu) |
|
return; |
|
|
|
/* |
|
* Currently trace_clock_local() calls sched_clock() and the |
|
* generic version is not NMI safe. |
|
*/ |
|
if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) { |
|
if (enter) |
|
nmi_ts_start = time_get(); |
|
else |
|
nmi_total_ts = time_get() - nmi_ts_start; |
|
} |
|
|
|
if (enter) |
|
nmi_count++; |
|
} |
|
|
|
/** |
|
* get_sample - sample the CPU TSC and look for likely hardware latencies |
|
* |
|
* Used to repeatedly capture the CPU TSC (or similar), looking for potential |
|
* hardware-induced latency. Called with interrupts disabled and with |
|
* hwlat_data.lock held. |
|
*/ |
|
static int get_sample(void) |
|
{ |
|
struct trace_array *tr = hwlat_trace; |
|
time_type start, t1, t2, last_t2; |
|
s64 diff, total, last_total = 0; |
|
u64 sample = 0; |
|
u64 thresh = tracing_thresh; |
|
u64 outer_sample = 0; |
|
int ret = -1; |
|
|
|
do_div(thresh, NSEC_PER_USEC); /* modifies interval value */ |
|
|
|
nmi_cpu = smp_processor_id(); |
|
nmi_total_ts = 0; |
|
nmi_count = 0; |
|
/* Make sure NMIs see this first */ |
|
barrier(); |
|
|
|
trace_hwlat_callback_enabled = true; |
|
|
|
init_time(last_t2, 0); |
|
start = time_get(); /* start timestamp */ |
|
|
|
do { |
|
|
|
t1 = time_get(); /* we'll look for a discontinuity */ |
|
t2 = time_get(); |
|
|
|
if (time_u64(last_t2)) { |
|
/* Check the delta from outer loop (t2 to next t1) */ |
|
diff = time_to_us(time_sub(t1, last_t2)); |
|
/* This shouldn't happen */ |
|
if (diff < 0) { |
|
pr_err(BANNER "time running backwards\n"); |
|
goto out; |
|
} |
|
if (diff > outer_sample) |
|
outer_sample = diff; |
|
} |
|
last_t2 = t2; |
|
|
|
total = time_to_us(time_sub(t2, start)); /* sample width */ |
|
|
|
/* Check for possible overflows */ |
|
if (total < last_total) { |
|
pr_err("Time total overflowed\n"); |
|
break; |
|
} |
|
last_total = total; |
|
|
|
/* This checks the inner loop (t1 to t2) */ |
|
diff = time_to_us(time_sub(t2, t1)); /* current diff */ |
|
|
|
/* This shouldn't happen */ |
|
if (diff < 0) { |
|
pr_err(BANNER "time running backwards\n"); |
|
goto out; |
|
} |
|
|
|
if (diff > sample) |
|
sample = diff; /* only want highest value */ |
|
|
|
} while (total <= hwlat_data.sample_width); |
|
|
|
barrier(); /* finish the above in the view for NMIs */ |
|
trace_hwlat_callback_enabled = false; |
|
barrier(); /* Make sure nmi_total_ts is no longer updated */ |
|
|
|
ret = 0; |
|
|
|
/* If we exceed the threshold value, we have found a hardware latency */ |
|
if (sample > thresh || outer_sample > thresh) { |
|
struct hwlat_sample s; |
|
|
|
ret = 1; |
|
|
|
/* We read in microseconds */ |
|
if (nmi_total_ts) |
|
do_div(nmi_total_ts, NSEC_PER_USEC); |
|
|
|
hwlat_data.count++; |
|
s.seqnum = hwlat_data.count; |
|
s.duration = sample; |
|
s.outer_duration = outer_sample; |
|
s.timestamp = CURRENT_TIME; |
|
s.nmi_total_ts = nmi_total_ts; |
|
s.nmi_count = nmi_count; |
|
trace_hwlat_sample(&s); |
|
|
|
/* Keep a running maximum ever recorded hardware latency */ |
|
if (sample > tr->max_latency) |
|
tr->max_latency = sample; |
|
} |
|
|
|
out: |
|
return ret; |
|
} |
|
|
|
static struct cpumask save_cpumask; |
|
static bool disable_migrate; |
|
|
|
static void move_to_next_cpu(bool initmask) |
|
{ |
|
static struct cpumask *current_mask; |
|
int next_cpu; |
|
|
|
if (disable_migrate) |
|
return; |
|
|
|
/* Just pick the first CPU on first iteration */ |
|
if (initmask) { |
|
current_mask = &save_cpumask; |
|
get_online_cpus(); |
|
cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask); |
|
put_online_cpus(); |
|
next_cpu = cpumask_first(current_mask); |
|
goto set_affinity; |
|
} |
|
|
|
/* |
|
* If for some reason the user modifies the CPU affinity |
|
* of this thread, than stop migrating for the duration |
|
* of the current test. |
|
*/ |
|
if (!cpumask_equal(current_mask, ¤t->cpus_allowed)) |
|
goto disable; |
|
|
|
get_online_cpus(); |
|
cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask); |
|
next_cpu = cpumask_next(smp_processor_id(), current_mask); |
|
put_online_cpus(); |
|
|
|
if (next_cpu >= nr_cpu_ids) |
|
next_cpu = cpumask_first(current_mask); |
|
|
|
set_affinity: |
|
if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */ |
|
goto disable; |
|
|
|
cpumask_clear(current_mask); |
|
cpumask_set_cpu(next_cpu, current_mask); |
|
|
|
sched_setaffinity(0, current_mask); |
|
return; |
|
|
|
disable: |
|
disable_migrate = true; |
|
} |
|
|
|
/* |
|
* kthread_fn - The CPU time sampling/hardware latency detection kernel thread |
|
* |
|
* Used to periodically sample the CPU TSC via a call to get_sample. We |
|
* disable interrupts, which does (intentionally) introduce latency since we |
|
* need to ensure nothing else might be running (and thus preempting). |
|
* Obviously this should never be used in production environments. |
|
* |
|
* Currently this runs on which ever CPU it was scheduled on, but most |
|
* real-world hardware latency situations occur across several CPUs, |
|
* but we might later generalize this if we find there are any actualy |
|
* systems with alternate SMI delivery or other hardware latencies. |
|
*/ |
|
static int kthread_fn(void *data) |
|
{ |
|
u64 interval; |
|
bool initmask = true; |
|
|
|
while (!kthread_should_stop()) { |
|
|
|
move_to_next_cpu(initmask); |
|
initmask = false; |
|
|
|
local_irq_disable(); |
|
get_sample(); |
|
local_irq_enable(); |
|
|
|
mutex_lock(&hwlat_data.lock); |
|
interval = hwlat_data.sample_window - hwlat_data.sample_width; |
|
mutex_unlock(&hwlat_data.lock); |
|
|
|
do_div(interval, USEC_PER_MSEC); /* modifies interval value */ |
|
|
|
/* Always sleep for at least 1ms */ |
|
if (interval < 1) |
|
interval = 1; |
|
|
|
if (msleep_interruptible(interval)) |
|
break; |
|
} |
|
|
|
return 0; |
|
} |
|
|
|
/** |
|
* start_kthread - Kick off the hardware latency sampling/detector kthread |
|
* |
|
* This starts the kernel thread that will sit and sample the CPU timestamp |
|
* counter (TSC or similar) and look for potential hardware latencies. |
|
*/ |
|
static int start_kthread(struct trace_array *tr) |
|
{ |
|
struct task_struct *kthread; |
|
|
|
kthread = kthread_create(kthread_fn, NULL, "hwlatd"); |
|
if (IS_ERR(kthread)) { |
|
pr_err(BANNER "could not start sampling thread\n"); |
|
return -ENOMEM; |
|
} |
|
hwlat_kthread = kthread; |
|
wake_up_process(kthread); |
|
|
|
return 0; |
|
} |
|
|
|
/** |
|
* stop_kthread - Inform the hardware latency samping/detector kthread to stop |
|
* |
|
* This kicks the running hardware latency sampling/detector kernel thread and |
|
* tells it to stop sampling now. Use this on unload and at system shutdown. |
|
*/ |
|
static void stop_kthread(void) |
|
{ |
|
if (!hwlat_kthread) |
|
return; |
|
kthread_stop(hwlat_kthread); |
|
hwlat_kthread = NULL; |
|
} |
|
|
|
/* |
|
* hwlat_read - Wrapper read function for reading both window and width |
|
* @filp: The active open file structure |
|
* @ubuf: The userspace provided buffer to read value into |
|
* @cnt: The maximum number of bytes to read |
|
* @ppos: The current "file" position |
|
* |
|
* This function provides a generic read implementation for the global state |
|
* "hwlat_data" structure filesystem entries. |
|
*/ |
|
static ssize_t hwlat_read(struct file *filp, char __user *ubuf, |
|
size_t cnt, loff_t *ppos) |
|
{ |
|
char buf[U64STR_SIZE]; |
|
u64 *entry = filp->private_data; |
|
u64 val; |
|
int len; |
|
|
|
if (!entry) |
|
return -EFAULT; |
|
|
|
if (cnt > sizeof(buf)) |
|
cnt = sizeof(buf); |
|
|
|
val = *entry; |
|
|
|
len = snprintf(buf, sizeof(buf), "%llu\n", val); |
|
|
|
return simple_read_from_buffer(ubuf, cnt, ppos, buf, len); |
|
} |
|
|
|
/** |
|
* hwlat_width_write - Write function for "width" entry |
|
* @filp: The active open file structure |
|
* @ubuf: The user buffer that contains the value to write |
|
* @cnt: The maximum number of bytes to write to "file" |
|
* @ppos: The current position in @file |
|
* |
|
* This function provides a write implementation for the "width" interface |
|
* to the hardware latency detector. It can be used to configure |
|
* for how many us of the total window us we will actively sample for any |
|
* hardware-induced latency periods. Obviously, it is not possible to |
|
* sample constantly and have the system respond to a sample reader, or, |
|
* worse, without having the system appear to have gone out to lunch. It |
|
* is enforced that width is less that the total window size. |
|
*/ |
|
static ssize_t |
|
hwlat_width_write(struct file *filp, const char __user *ubuf, |
|
size_t cnt, loff_t *ppos) |
|
{ |
|
u64 val; |
|
int err; |
|
|
|
err = kstrtoull_from_user(ubuf, cnt, 10, &val); |
|
if (err) |
|
return err; |
|
|
|
mutex_lock(&hwlat_data.lock); |
|
if (val < hwlat_data.sample_window) |
|
hwlat_data.sample_width = val; |
|
else |
|
err = -EINVAL; |
|
mutex_unlock(&hwlat_data.lock); |
|
|
|
if (err) |
|
return err; |
|
|
|
return cnt; |
|
} |
|
|
|
/** |
|
* hwlat_window_write - Write function for "window" entry |
|
* @filp: The active open file structure |
|
* @ubuf: The user buffer that contains the value to write |
|
* @cnt: The maximum number of bytes to write to "file" |
|
* @ppos: The current position in @file |
|
* |
|
* This function provides a write implementation for the "window" interface |
|
* to the hardware latency detetector. The window is the total time |
|
* in us that will be considered one sample period. Conceptually, windows |
|
* occur back-to-back and contain a sample width period during which |
|
* actual sampling occurs. Can be used to write a new total window size. It |
|
* is enfoced that any value written must be greater than the sample width |
|
* size, or an error results. |
|
*/ |
|
static ssize_t |
|
hwlat_window_write(struct file *filp, const char __user *ubuf, |
|
size_t cnt, loff_t *ppos) |
|
{ |
|
u64 val; |
|
int err; |
|
|
|
err = kstrtoull_from_user(ubuf, cnt, 10, &val); |
|
if (err) |
|
return err; |
|
|
|
mutex_lock(&hwlat_data.lock); |
|
if (hwlat_data.sample_width < val) |
|
hwlat_data.sample_window = val; |
|
else |
|
err = -EINVAL; |
|
mutex_unlock(&hwlat_data.lock); |
|
|
|
if (err) |
|
return err; |
|
|
|
return cnt; |
|
} |
|
|
|
static const struct file_operations width_fops = { |
|
.open = tracing_open_generic, |
|
.read = hwlat_read, |
|
.write = hwlat_width_write, |
|
}; |
|
|
|
static const struct file_operations window_fops = { |
|
.open = tracing_open_generic, |
|
.read = hwlat_read, |
|
.write = hwlat_window_write, |
|
}; |
|
|
|
/** |
|
* init_tracefs - A function to initialize the tracefs interface files |
|
* |
|
* This function creates entries in tracefs for "hwlat_detector". |
|
* It creates the hwlat_detector directory in the tracing directory, |
|
* and within that directory is the count, width and window files to |
|
* change and view those values. |
|
*/ |
|
static int init_tracefs(void) |
|
{ |
|
struct dentry *d_tracer; |
|
struct dentry *top_dir; |
|
|
|
d_tracer = tracing_init_dentry(); |
|
if (IS_ERR(d_tracer)) |
|
return -ENOMEM; |
|
|
|
top_dir = tracefs_create_dir("hwlat_detector", d_tracer); |
|
if (!top_dir) |
|
return -ENOMEM; |
|
|
|
hwlat_sample_window = tracefs_create_file("window", 0640, |
|
top_dir, |
|
&hwlat_data.sample_window, |
|
&window_fops); |
|
if (!hwlat_sample_window) |
|
goto err; |
|
|
|
hwlat_sample_width = tracefs_create_file("width", 0644, |
|
top_dir, |
|
&hwlat_data.sample_width, |
|
&width_fops); |
|
if (!hwlat_sample_width) |
|
goto err; |
|
|
|
return 0; |
|
|
|
err: |
|
tracefs_remove_recursive(top_dir); |
|
return -ENOMEM; |
|
} |
|
|
|
static void hwlat_tracer_start(struct trace_array *tr) |
|
{ |
|
int err; |
|
|
|
err = start_kthread(tr); |
|
if (err) |
|
pr_err(BANNER "Cannot start hwlat kthread\n"); |
|
} |
|
|
|
static void hwlat_tracer_stop(struct trace_array *tr) |
|
{ |
|
stop_kthread(); |
|
} |
|
|
|
static bool hwlat_busy; |
|
|
|
static int hwlat_tracer_init(struct trace_array *tr) |
|
{ |
|
/* Only allow one instance to enable this */ |
|
if (hwlat_busy) |
|
return -EBUSY; |
|
|
|
hwlat_trace = tr; |
|
|
|
disable_migrate = false; |
|
hwlat_data.count = 0; |
|
tr->max_latency = 0; |
|
save_tracing_thresh = tracing_thresh; |
|
|
|
/* tracing_thresh is in nsecs, we speak in usecs */ |
|
if (!tracing_thresh) |
|
tracing_thresh = last_tracing_thresh; |
|
|
|
if (tracer_tracing_is_on(tr)) |
|
hwlat_tracer_start(tr); |
|
|
|
hwlat_busy = true; |
|
|
|
return 0; |
|
} |
|
|
|
static void hwlat_tracer_reset(struct trace_array *tr) |
|
{ |
|
stop_kthread(); |
|
|
|
/* the tracing threshold is static between runs */ |
|
last_tracing_thresh = tracing_thresh; |
|
|
|
tracing_thresh = save_tracing_thresh; |
|
hwlat_busy = false; |
|
} |
|
|
|
static struct tracer hwlat_tracer __read_mostly = |
|
{ |
|
.name = "hwlat", |
|
.init = hwlat_tracer_init, |
|
.reset = hwlat_tracer_reset, |
|
.start = hwlat_tracer_start, |
|
.stop = hwlat_tracer_stop, |
|
.allow_instances = true, |
|
}; |
|
|
|
__init static int init_hwlat_tracer(void) |
|
{ |
|
int ret; |
|
|
|
mutex_init(&hwlat_data.lock); |
|
|
|
ret = register_tracer(&hwlat_tracer); |
|
if (ret) |
|
return ret; |
|
|
|
init_tracefs(); |
|
|
|
return 0; |
|
} |
|
late_initcall(init_hwlat_tracer);
|
|
|